refactoring: compilation warnings

Add options for showing these warnings during the compilation.
FormulaComponent abstract class is now parameterized.
Change the way to open a File in the FileHelper (safer). The resource is now opened directly in the method for improving the readability.

refactoring: preStart/postStop, call to super methods (safer)

refactoring: update licence header

refactoring: add the target list inside the Monitor object

refactoring: change TargetUsageRatio.percent to ratio